Snap action electric switch mechanism



P. G. HUGHES 2 SHEETS-SHEET 1 Inventor Li 5 6. His Attorney.

Ph' Hughes, b9 my March 17, 1953 SNAP ACTION ELECTRIC SWITCH MECHANISM Original Filed Jan. 18. 1949 March 17, 1953 P. G. HUGHES SNAP ACTION ELECTRIC SWITCH MECHANISM 2 SHEETSSHEET 2 Original Filed Jan. 18. 1949 invehtbr: PhiLip Ci. Hughes, @4 ,XVhT. by His Attorney.

Patented Mar. 17, 1953 SNAP ACTION ELECTRICSWITCH MECHANISM Philip G. Hughes, Schenectady,"N. Y., assignor to General Electric Company, a corporation of New York Original application January 18, 1949, Serial No. 71,504. Divided and this application March 16, 1950, Serial No. 150,051

6 Claims. 1

My invention relates to snap action electric switches and the like, and more particularly to manual reset means for an interlocked pair of thermal timing switches. Switches embodying my invention are especially suited to the control and protection of fluid fuel burners and the like.

It is a general object of my invention to provide a new and improved snap action electric switch mechanism, and particularly a switch mechanism which is inexpensive and readily assembled, as well as durable and reliable in operation.

'It is'a further object of my invention to provide new and improved means for resetting a double acting snap action switch, and especially to provide such resetting means particularly suitable to thermally actuated switches.

It is a particular object of my invention to provide a new and improved dual thermal timing switch for controlling lockout and recycling in a fluid fuel burner control system.

My invention itself will loe'rnore fully understood and its various objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawings, in which Fig. 1 is a diagrammatic illustration of a burner control apparatus embodying my invention, showing the thermal timing apparatus in exploded perspective view; Fig. 2 is a side elevational view of the thermal timing apparatus :of Fig. 1, shown with the parts in assembled relation; and Fig. 3 is a schematic circuit diagram of the burner control system shown at Fig. 1 as illustrative of one applicationof my timer.

.Referring now to the drawingsand particularly to'Fig. l, I have illustrated one preferred embodiment ofmy invention applied to the control of an oil burning apparatus comprising a pump motor 1., an ignition transformer .2, an oil supply nozzle 3 and a pair of ignition electrodes 4. The operation of the burner apparatus, and particularly the operation of the motor I and ignition transformer 2, is controlled by a room thermostat 5, a transformer relay 8, a flame detector 'i and a thermal timing apparatus 8. The new and novel features of my improved thermal timing apparatus are best described against the background of an oil burner control system, to which it is typically applicable. For this reason, the control system shown at Figs. land 3'wil1 be first described. This system is described and claimed in a copending application Serial No. 73,293, filed by Jack Witherspoon' for Control System for Fluid Fuel Burners, on January 28,

194l9,-and assigned to the sameassignee .as the present application. The flame detector 1 is fully described :and claim'ed in .my c'opending application Serial No. 74,786, filed on February 5, 1949, now Patent No. 2,512,331, issued June 20, 1950, for Thermal Responsive Switch.

Referring now to Fig. 3, I have shown the motor t and ignition transformer 2 connected for energization in parallel circuit relation through normally open contacts to of the relay 8. The parallel circuit through the ignition transformer '2 includes a normally closed contact 9 of the thermal timer 8. Through the relay contactfia, the motor and ignition transformer are connected to -a pair of supply conductors H1. The conductors l0 are connected to a source of alternating current'supply (not shown) which, for normal home operation, may suitably be I of the 110 volt, 60 cycle type.

The transformer relay 6 is preferably of the type more fully described and claimed in the pending applications Serial No. 794,297, filed by Philip Hughes on December 29,1947, now Patent 2,527,220, issued October 24, 1950, and Serial No. 794,298, filed by Philip H. Estes on December 29, 1947,;now abandoned, both of which are assigned to the same assignee as the instant :application. This-relay comprises a three-legged magnetizable core having a movable outer leg or armature H, a low voltage secondary winding 12 on the center leg and a high voltage primary winding it .on the stationary outer leg. The, primary winding 13 of the transformer relay 6 connected across the supply conductors i0 and the secondary winding 12 .is connected to be completedor short .circuited through a series circuit includingthe room thermostat 5 and a pairof thermal timers M and I5 (Fig. 3) include'din the thermal timing apparatus 8.. This series circuit includes the room thermostat 5, a normally open holding contact 16 of the transformer relayfi, an electric heating resistor 11 of the thermal timer M, a normally closed contact 18 of the thermal timer M, a normally closed contact 19 of the thermal timer l5 and an electric heating resistor 20 of the thermal timer [5. The thermal timers M and I5 are connected in electrically interlocked relation through the hot and cold contacts 21 and 22, respectively, of the flame detector 1, so that the electric heating resistors H and 2 0 are effectively energized only alternatively. More particularly, the flame detector 7 is provided with a movable contact 23 arranged, when in engagement with the 'cold contact 22. to shunt the heating resistor I! and the relay holding contact IS. The flame detector contact 23, when in engagement with the hot contact 2!, provides a shunt circuit around the heating resistor 20 and the normally closed thermal timer contacts l8 and it. The thermal timer I4 is connected to actuate also the normally closed ignition transformer contact 9.

In the foregoing arrangement illustrated at'] Fig. 3, the thermal timer i5 serves as a lockout timer, in that opening of its normally closed contact l9 eifects deenergization of the burner motor I and ignition transformer 2. The thermal timer l4 serves as a recycling and ignition timer, in that its contact 9 controls the ignition shutoff and its contact l8 controls the scavenging time, or delay interval, between flame failure and reinitiation of burner operation. To facilitate this operation, the heating time of the flame detector 2' is less than the heating time of the thermal lockout timer I5, and the cooling time of the flame detector 1 is less than the cooling time of the thermal recycling timer M. Moreover, the resistance of the electric heating resistors I! and 2% is such that when both these resistors are in series in -the circuit of the relay Winding l2 insufficient current flows in the winding to pick up the relay, but sufficient current is carried through the heating resistors Ill and 2E in series to hold the relay armature I l in its attracted position, if previously picked up. It will,

of course, be understood that, within the scope of my invention, the circuit may be so connected that the heating resistors are never energized in series circuit relation.

The operation of the control system shown at Fig. 3 is as follows: Starting with the apparatus in its fully deenergized position, as shown, let it be assumed that the room thermostat 5 closes in response to a call for heat. Upon closure of the room thermostat 5, the normally open secondary winding iii of the transformer relay 6 is completed through the room thermostat 5, the lockout heating resistor 28, the normally closed lockout contact it, the normally closed recycling contact IS, and the normally closed cold contacts 22, 23 of the flame detector 1. Upon completion of the secondary winding l2, the relay armature H is attracted and closes the contacts 6a and I6. Closure of the contact 8a completes an energizing circuit for the motor i and the primary winding of the ignition transformer 2, the ignition transformer circuit including the normally closed thermal timer contact 9. Thus, the oil burner is set into operation. Closure of the relay contact I t completes a holding circuit for the relay coil l2 in anticipation of opening of the flame detector cold contacts 22, 23.

If the oil is properly ignited, the resulting flame heats the flame detector 1 and the movable contact 23 leaves the cold contact 22. Prior to such flame detector contact separation, the lookout heater 2!! was fully energized, so that if no flame had occurred, the lookout contact it would have timed open after a predetermined interval, thereby to open the circuit of the relay winding I2 and deenergize the burner. Under normal starting operation, however, as soon as the cold contacts 22, 23 of the flame detector are separated, the heating resistor F5 is thrown in series circuit relation with the heating resistor 20 through the holding contact l6, thereby to reduce the current in the circuit of the relay winding 12. This reduced current is insuflicient to pick up the relay armature i l, but is sufficient to hold it in attracted position. The armature i I is thus 4 held attracted during the flame detector transfer interval when both heating resistors I1 and 2d are in series. The reduced current in the series circuit through the winding l2 and the heaters H and 21? during this transfer interval is also insuflicient to appreciably heat the thermal timers M and 55, so that progress of the thermal timer 15 toward the lockout position is arrested as soon as the flame detector cold contacts 22, 23 are separated.

If flame continues in the burner uninterrupted. the flame detector movable contact 23 arrives, after a brief interval, at a position of contact engagement with the flame detector hot contact 2|. In this position, a shunt circuit is provided through the hot contacts 2|, 23 around the series connected thermal timer contacts [8 and i 9 and the resistance heater 2%. The lockout heater 29 being thus short circuited begins to cool, and the recycling and ignition timer heater ll, being now fully-energized by short circuiting of the heater it, heats up to time its contacts 9 and it open. When the contacts 9 and I8 are opened after a predetermined delay interval,- the ignition transformer 2 is deenergized by opening of the contact at. Opening of the contact [8 has no immediate eflect, because this contact is in a series circuit which is presently short circuited through the hot contact 2| of the flame detector I.

If the burner shuts down normally due to opening of the room thermostat 5, the circuit of the relay winding 12 is simply opened at the room thermostat 5, and the relay dropped out to shut down the burner. If, however, flame failure should occur for any reason before the room thermostat 5 opens, the circuit of the relay winding i2 is opened by separation of the flame detector contacts 2!, 23. Under conditions of flame outtage, whether it be due to normal shutdown by the room thermostat or to flame failure or other cause, the flame detector movable contact 23 responds relatively rapidly by leaving the hot contact 2! and engaging the cold contact 22.

If flame failure is due to some cause other than normal shutdown by the room thermostat 5, so that the room thermostat is still closed, reengagement of the flame detector cold contacts 22 and 23 will not immediately restart the burner. The necessary delay interval between flame failure and recycling, which interval is allowed for scavenging of combustible gases from the furnace chamber, is controlled not by the flame detector '5, but by the slower cooling recycling timer l i. As previously stated, the cooling time of the thermal-timer i4 is longer than that of the flame detector. Moreover, the cooling'time of the timer it is substantially independent of the conditions under which flame failure occurs, and therefore ensures a substantially constant predetermined scavenging time. It will be evident that, if flame failure occurs with the room thermostat 5 closed, recycling is initiated as soon as the thermal timer M recloses its contact i8 after the cooling interval.

Referring now more particularly to Figs. 1 and 2, I have illustrated in detail a preferred form of thermal timer structure embodying my invention. In this timer, the lockout and recycling timers i5 and i l,,respectively, are mechanically interlinked to provide ambient temperature compensation, as well as compensation of the timer for thermal resistance variations in the heating circuit and protective interlockin ofthe timer reset mechanism.

5 From Figs. 1 and 2, it is evidentthat the "combined. recycling and lockout timer 8 comprises a pair of elongated thermally deformable bi.

metallic strips 58a and 19a, each fixed atone end to a pivotally mounted movable supporting block 25 and extending outwardly therefrom in parallel spaced relation. The block. 25 is "rotatably mounted on a base 28, and the extending end of the bimetallic strip 19a is held fixed relative to the base by means of an adjustable stop 21. The free end of the bimetallic strip |3a is linked by a fiat strip of insulatingmaterial '23 to a pair of snap acting overcentermechanisms 23 and 39.

Referring more particularly to Fig. 2;.thedual thermal timer 8 is mounted in a base or housing '28, preferably formed of a suitable moulded plastic insulating material, open at one side "and provided with the necessary abutments, aper tures and recesses to accommodate the various parts of the timer. Within the casing 26, the movable supporting block '25 is. rotatably mounted upon a pivot pin :31 projecting outwardly from the integral side wall of the casing. The bimetallic strips 33a and lea are mounted at their upper ends in cantilever fashion on opposite sides of the supporting block 25 ancldepend therefrom in substantially parallel spaced relation. The bimetallic strips are so disposed on the block that, if the block were held sta-- tionary and both strips heated, their free ends would move angularly in the same direction about the pivot pin '55 and block 2-5. That is, the bimetallic strips i850 and 19a tend to maintain parallelism when equally heated. However, the depending or free end of the bimetallic strip 19a is unable to move with respect to the casing 2i: because it is held fixed in the adjustable stop 27. The stop 2i is arranged to be moved slightly with respect to the casing 25 by a set screw 32.

The overcenter switch mechanisms or members 2% and 39 are each of the integral spring plate type and each comprises a spring plate slotted to provide a pair of outer tension members and a pair of inner aligned compression members, the abutting endsoi the compression members pivotally engaging a fixed or normally fixed supporting member. In the particular form of the switches herein shown, the outer tension strips of each switch member 2152 and are crimped to form tension springs which bias the central pivoted compression members to one side or the other of a dead-center position. The upper end of the overcenter switch member 22% carries the lookout contact 15, and the upper end of the overcenter switch member 3% is connected by an insulating link $3 to a pair of cantilever spring ccntact'arms '9 and :3 which constitute the ignition and recycling contacts. respectively. The lowermovable ends of the snap action switch members 23 and 39 areeach connected by the actuating link 2% to the depending free end of the bimetallic strip 1.8a. Snap action switch members of this type claimed in Patent 2,429,813, issued to George M. Hausler on October 29, 1947.

The overoenter snap action switch member as is pivotally mounted at its center upon stationr ary but adjustable support as. The pivotal support S 1 projecting of an L-shaped mounting bracket 35. The mounting bracket 35 is positioneo'. with one of the i. lying in a .rectangular recess 35 in the integral side wall of the casing 26. The bracket Sbis fixed in posiis formed as an ear turned out from the directions.

tion by bolt .37, and is adjustable; within the range permitted. by an elongated hole or slot 38 in the casing side wall through which the bolt 3? passes. The contact carrying end of the snap action switch member 219 stops in one direction of movement against a fixed contact l-Eband in the other direction of movement against an abutment 23% formed integrally with the-casing 26.

The snap action switch-member so is mounted at its center upon the slidable shank iii of a reset button i il which projects through an aperture in the front wall of the casing 26. The head of the reset button A! is slidably mounted in the front wall of the casing 26, and the inner .end'of the shank :E-ii is slidably mounted. in an aperture formed at the upper end of an internal insulating support 42. The suppom or bracket 42 is fixed on the side wall of the casing 25 in substantially parallel spaced relation with the front casing wall. The fixed bracket 42 serves also as a support for the cantilever contact springs i and it. The reset button shank All is provided in ermediate its ends with a pair of oppositely projecting shoulders -4;3,;-.and a helical compression spring 5 encircling the shank 46 is disposed between the shoulders 43 and the supporting bracket 42. The spring-4 biases the reset button 4%], e: to anormal position. in which a shoulder Ma abuts against the front casing wall. The reset button shank 45:] thus serves as a normally stationary support for the action switch member 6%. The'upper end of the switch member 3%? is stopped inone direction of movement by engagement of the contact springs and is wi h a pairof cooperating stationary contacts Sc and 18b, respectively, and in the other direction of movement by engagement of the insulating link at with the front wall of the casing 2s.

The loci-rout heater 2c is moiuited on the hi metallic strip intermediate its ends, and is preferably arranged. for relatively slow thermal response. In the form of the invention illustrated, the lockout heater 2% is of large ,diame ter relative to the cross sectional area of the bimetallic strip its, and is concentrated overa small length of the strip. Preferably, 'theheater 25 is wound upon a sleeve Eda formed of .a nat ural or artificial rubber having relatively poor thermal conductivity. The recycling heater H is mounted upon the bimetallic strip its intermediate its ends and is preferably arranged for a relatively quick thermal response. To this cred, the recycling heater i? is wound in relatively close thermal contact with the bimetallicstrip Elia, and is distributed along a considerable por tion of the length of the strip.

In the normal unheated condition of the mechanism shown in thedrawing, all the timer contacts 9, IS and 59 are closed, so that the overcenter biasing forces of the snap action switch members 29 and .39 are in opposition, i. -e., tend to move the switch link 25 in .theopposite The bimetallic strips Hiaancl iBc are so disposed on the movable supporting block .25 that, when heated, the strips move, or tend to move, their depending free ends toward the right, as viewed in the drawings. I

Inoperation, when the bimetallic strip 49:; is heated, it tends to move its depending tree-end toward the right. Such movement of the end of the strip 9c is, however, restrained by the stop 21, with the result that the strip its effects pivotal movement of the rotatablymounted supporting block 25 in a clockwise direction, as viewed in the drawings. Such clockwise rotation of the supporting block 25 moves the depending free end of the bimetallic strip 58a to the left, as viewed in the drawings. On the other hand, heating of the bimetallic strip its. causes its free end to move toward the right, thereby to counteract the rotational movement of the supporting block 25. Thus, it will be seen that, with the bimetallic strips 19a, and 18a extending outwardly from the pivotally mounted supporting block 25 and arranged to move or tend to move their free ends in the same angular direction with respect to the block when heated, an ambient temperature compensation is effected due to the action of the free strip in counteracting by its movement the deformation of the restrained strip.

The combined thermal timer shown at Fig. 2 is also compensated in its lockout action for resistance variations in the heater circuit due to temperature change in the lookout heater coil 20 and relay winding I2. Thus, a substantially constant predetermined lockout time is provided by the timer independently of the ambient temperature in which the lockout heating resistor 20 and the relay coil 52 are operating. This avoids lengthening of the lockout timing interval upon recycling when the lookout heater and relay coil are operating at relatively high ambient temperatures due to self-heat. For this purpose, the lockout bimetal [9a is made somewhat longer, for example, about four or five per cent longer, than the recycling bimetal 58a. Thus, the timer is not fully compensated or i slightly mismatched for changes in ambient temperature. Such mismatching produces a slight motion of the switch link 28 in the lookout direction upon increase of ambient temperature with no heating current flowing. motion in the lookout direction aids the lookout heater and compensates for the reduced heatercurrent in the lockout heater resulting from increased coil resistance under high ambient temperature conditions. By proper proportioning of the length of the bimetallic elements liia and l9a, the lookout delay interval may be made substantially the same over a considerable range of ambient temperature. Also, it will be understood that, by changing the degree of mismatching, the device may be compensated for resistance variations in both the lookout heater and the relay coil, or only in the lookout heater alone, depending upon the circuit used and the condition desired.

The normal operation of the thermal timer, shown at Fig. 2, in the system previously described in conjunction with Fig. 3, is as follows: Upon closure of the room thermostat 5, the recycling heater I! is short circuited and the lockout heater 20 energized. The bimetallic strip I9a is thus heated and deformed and the movable support 25 is rotated clockwise, thereby to move the switch link 28 toward the lockout position (to the left, as viewed in the drawings). This movement, however, is relatively slow due to the thermal characteristics of the lookout heater 20, so that if flame is established at the proper time, the flame detector 7 closes on its hot contact 2! before the lockout switch member 29 is snapped overcenter to open its contacts, thereby to short circuit the lookout heater and fully energize the recycling heater ll. Consequent heating of the recycling bimetal tea and cooling of-the lockout bimetal 19a reverses the This slight i1 motion of the switch link 28, thereby to move the link back toward its normal position and beyond this position (toward the right, as viewed at Fig. 2) to effect overcenter opening operation of the recycling and ignition switch member 30. Upon shutdown of the burner, for any cause, the recycling heater I! is deenergized and the bimetal I8a allowed to cool. During this cooling interval, the switch actuating link 28 is moved back toward its normal position, thereby to snap the switch member 30 overcenter and reclose the contacts 9 and l8. This reclosure interval of the contacts 9 and 18 upon cooling of the bimetallic strip IBa determines the recycling time, or scavenging interval, of the burner.

It will, of course, be understood that if, in the foregoing cycle, no flame is established, the flame detector 1 does not transfer its contacts. Under this condition, the recycling heater it remains short-circuited, and the lookout heater 20 merely continues to cause deformation of the bimetal 19a to a limiting lockout position. This action moves the switch link 28 to the left as viewed in the drawings until the lockout contact I9 is snapped open. As more fully explained hereinafter, cooling of the bimetal [9a from this lockout position does not cause automatic reclosure of the contact [9.

As previously noted, when the switch link 28 is in its normal position with both the lockout contact and the recycling contacts closed, the overcenter biasing forces of the snap action switch members 29 and 30 are applied to the switch link 28 in opposition. Consequently, when either one or the other of the switch members 29 or 30 is in its contact opening position, the overcenter biasing forces of both snap action switch members are applied in aiding relation to the switch link 28. In the open position of the switch member 36, these aiding overcenter forces are lIlSllfficient to overcome the appreciable return force of the resilient bimetallic member lBa as it is cooled. On the other hand, the normal position of the lockout switch member 29 is much closer to its dead-center position than are the corresponding positions of the switch member 30, so that when the lockout switch member is in its contact opening position, the bimetallic strip l8a is only slightly deformed and its return force is insuflicient to overcome the combined overcenter biasing forces of the two switch members 29 and 3B. This adjustment ensures that the lookout contact I9 will remain open after the thermal timer has cooled following lockout on flame failure. It is to reset the lockout switch member i9 that the reset button 4%, H is provided.

It will be noted that the reset button 40, 4| does not directly engage either the lookout switch member 29 or the switch link 28, but rather actuates the switch link 28 only through overcenter action of the snap action switch member 30. This is a safety feature which positively ensures opening of the contacts 9 and 18 prior to reclosure or resetting of the lookout contact I9. In resetting operation with the lookout contact l9 open, the reset button 40, M is pushed inwardly to move the normally stationary central pivot points of the snap action switch member 3G overcenter with respect to its end. By this movement, the switch member 38 is snapped to its open circuit position, thereby opening its contacts 9 and I8 and reversing its overcenter biasing force applied to the switch link 28. The thus reversed overcenter biasing force of the switch member 39 aids the return force of the bimetallic strip Ma, and together these forces are sufficient to overcome the opening bias of the lockout switch member 29, so that the switch link 28 is moved to the right, as viewed in the drawings, to snap the switch member 29 overcenter and reclose the lookout contact l9. The reset button iii, 4! is then released and returned to its normal position under the influence of-the return spring 44. In so returning to its normal-position, the reset button effects reclosing operation of the snap action switch member 35.

From the foregoing detailed description, it will now be evident that in the dual thermal timer shown at Fig. 2 it is not essential that the bimetallic strips iBa and 19a extend from the supporting block 25 in parallel spaced relation, but, if desired, these bimetallic strips may extend from the block 25 in any desired angular spaced relation. Moreover, it will be evident that the interlocking reset arrangement described above in conjunction with the two snap action switch members 29 and 30 is not limited in its application to an ambient temperature compensated thermal timer, but is equally applicable to any oppositely disposed pair of overcenter switch members actuated by a common actuating member.

My present application is a division of my copending application Serial No. 71,504, filed J anuary 18, 1949, and entitled Thermal Timing Apparatus, wherein the ambient temperature compensated thermal timer is more particularly claimed.

While I have described and illustrated only a preferred embodiment of my invention by way of example, many modifications will occur to those skilled in the art, and I, therefore, wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric switch, a movable actuating member, resilient means for operating said member to either side of a predetermined intermediate normal position, a pair of overcenter switch mechanisms coupled to said actuating member for actuation respectively upon movement of said member in one or the other direction, the combined forces of the said switch mechanisms being sufficient to return said actuating member to the said intern ediate position from a first actuated position but not from the second actuated position, and manually operable means for actuating the switch mechanism not actuated in said second position from its normal position independently of the location of said switch actuating member.

2. In an electric switch, a movable actuating member, resilient means for moving said member in opposite directions from an intermediate normal position to two spaced apart end positions, a pair of overcenter switch mechanisms disposed to be actuated by said actuating member in said end positions respectively, the resilience of said actuating member in one of said end positions being insufiicient to overcome the additive overcenter loading of both said switch mechanisms, and manually operable means independent of said actuating member for actuating overcenter that switch mechanism unaffected by said movement of said actuating member to said one end position.

3. In an electric switch, a movable actuating member, resilient means for moving said member to either side of a predetermined intermediate normal position, a pair of overcenterswitch mechanisms coupled to said actuating member and normally disposed on opposite sides of their dead-center positions, said dead-center positions being unequally spaced from the normal positions of saidswitch mechanisms whereby said mechanisms areactuable upon unequal movements of said actuating-member in'opposite directions from its normal position, and manually operable means movable independently of saidactuatingmember to effect overcenter operation of that switch mechanism normally most remote from its deadcenter position.

4. In an electric switch, a movable actuating member, resilient means for moving said member in opposite directions from an intermediate normal position to two spaced apart switch actuating positions, a pair of overcenter switch mechanisms normally disposed at unequal distances on opposite sides of their dead-center positions and coup-led for actuating to said actuating member, the overcenter loading of said switch actuating mechanisms being applied to said switching actuating member in opposing relation in the normal position of said switch actuating member and being applied to said switch actuating member in aiding relation in each of said switch actuating positions of said actuating member, said resilient means having sufficient return force to reset said switch mechanism normally most remote from its dead-center position and having insuiiicient return force to reset the other of said switch mechanisms, and manually operable means movable independently of said switch actuating member for effecting overcenter operation of said normally remote switch mechanism thereby to reverse its overcenter loading and reset said other switch mechanism.

5. In a thermal switch, a movable switch actuating member, a resilient thermally deformable member connected to move said switch actuating member in opposite directions from an intermediate normal position to two spaced apart switch actuating positions, a pair of overcenter switch mechanisms each comprising an integral slotted spring plate coupled for actuation to said switch actuating member, said spring plates being normally disposed on opposite sides of their deadcenter positions so that in the normal position of said switch member the overcenter loading of said spring plates is applied in opposition to said switch member, the normal position of said switch member being unequally spaced from the deadcenter positions of said spring plates and the return force of said thermally deformable member being suiiicient to reset the normally most remote spring plate but insufficient to reset the other said spring plate, and manually operable means movable independently of said switch actuating member to effect overcenter movement of said normally remote spring plate thereby to reverse the loading applied by it to said actuating member, whereby said reverse loading aids the return force of said deformable member and effects resetting of the other said spring plate.

6. In an electric switch, an actuating member movable substantially rectilinearly, means including a cantilever mounted resilient member for operating said actuating member to either side of a predetermined intermediate position, a pair of overcenter switch mechanisms coupled to said actuating member for actuation respectively upon movement of said member in one or the other direction, the combined forces of the said two switch mechanisms being suiiicient to return said 11 12 actuating member to the said intermediate posi- REFERENCES CITED tion from a first actuated position but not from The following references are of record in the the sec-0nd actuated position, and manually opme of this erable means for actuating the switch mechanism not actuated in said second actuated posi- 5 UNITED STATES PATENTS tion overcenter from its normal position when Number Name Date said actuating member is in the said second actu- 2,242,769 Werner May 20, 1941 ated position thereby to return said actuating 2,394,714 Newton Feb. 12, 1946 member from the second actuated position to 2,485,340 Warmey Oct. 18, 1949 said intermediate position. 10

PHILIP G. HUGHES. 

